The invention relates to a vacuum valve comprising a valve housing with an interior and first and second valve openings which are surrounded by first and second seat surfaces, and a closure unit arranged in the interior of the valve housing, said closure unit having a first plate, a second plate, a roller carrier arranged between the first plate and the second plate, a plurality of roller pairs which are each formed by a first spreading roller and a second spreading roller which are mounted on the roller carrier so as to be rotatable about respective axes of rotation, and at least one spring by which the first and second plates are pulled against the spreading rollers, which bear against mutually facing surfaces of the first and second plates, wherein the roller carrier is displaceable, parallel to a displacement direction, from an open position, in which the vacuum valve is open and the first and second valve openings are cleared, via an intermediate position, in which the first and second plates are located between the first and second valve openings but are spaced apart from the first and second seat surfaces, into a closed position, in which the vacuum valve is closed, and during the displacement of the roller carrier from the open position into the intermediate position, the first and second plates are carried along by the roller carrier, and during the displacement of the roller carrier from the intermediate position into the closed position, any further displacement of the first and second plates in the displacement direction is blocked, wherein, in the open position and intermediate position of the roller carrier, the first spreading roller of each roller pair bears against the surface of the first plate in the region of a respective recess in the surface of the first plate, and the second spreading roller of each roller pair bears against the surface of the second plate in the region of a respective recess in the surface of the second plate, and during the displacement of the roller carrier from the intermediate position into the closed position, the first and second spreading rollers are displaced along rising flanks of the recesses and in the process spread apart the first and second plates parallel to a spreading direction.
Vacuum valves of this kind, also referred to as slide valves, having closure units that are able to be spread apart are known in various embodiments. In a common embodiment, balls are used to spread apart the two plates of the closure unit, said balls being arranged in pairs in a ball cage arranged between the two plates. In the moved-together state of the closure unit, the balls project into recesses in the plates. In order to spread the plates apart, the ball cage is displaced with respect to the plates, wherein the balls are guided at least partially out of the recesses in the plates. Configurations of this kind can be gathered for example from U.S. Pat. Nos. 4,052,036 A, 5,379,983 A, 3,368,792 A and CH 508 154 A.
Instead of balls arranged in a ball cage, the use of spreading rollers is also already known, said spreading rollers being mounted on a roller carrier, arranged between the first and the second plate, so as to be rotatable about axes of rotation. Wear can be reduced as a result. In order that the forces required to spread the first and second plates apart are each introduced into the same regions of the roller carrier, the spreading rollers are arranged in pairs as roller pairs. Of each roller pair, the first spreading roller cooperates with the first plate and the second spreading roller cooperates with the second plate.
A vacuum valve of this kind, of the type mentioned at the beginning, can be gathered from CN 204 26 77 68 U.
A drawback of the use of spreading rollers instead of balls is the relatively large overall size of the closure unit with regard to its total thickness (=extension in the spreading direction). When the spreading rollers are mounted on their axle pins so as to slide, there is the risk that, due to the friction conditions that arise, the spreading rollers will slide over the plate surfaces during the spreading apart of the first and second plates, rather than rolling over them, this in turn resulting in increased wear. The use of spreading rollers mounted on rolling elements requires a much greater diameter of the spreading rollers, however, with the result that the thickness of the closure unit would be increased further.